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Abstract

The number of instrumental ground motion records in New Zealand (NZ) has increased significantly in recent years due to an increase in the
number and quality of seismometer throughout NZ. Figure 1 provides a comparison between NGA ground motion database and the NZ
database developed as part of this study. Despite this increase in instrumental data, it can be seen clearly in Figure 1 that there is a lack of
empirical records from large magnitude events observed at near-source distances. This is even more clear in Figure 2, which plots the
cumulative number of records exceeding specific PGA values in the NZ ground motion database. There are only a total of 66 ground motion
records which have PGA values above 0.1g (28 crustal, 11 interface, and 27 slab). Furthermore, the maximum PGA values recorded are
0.39g, 0.31g, and 0.28g for crustal, interface, and slab events, respectively. This lack of ground motion records from large magnitude nearsource
records, which typically dominate seismic hazard analyses, makes it difficult to develop robust ground motion prediction equations
used in seismic hazard analysis based on NZ data alone.
In this study an alternative approach to empirical ground motion prediction equation development was taken. Firstly, the applicability of
various foreign ground motion prediction equations (derived using plentiful data) to NZ were considered. The consideration was based on
both the dependence of the inter- and intra-event residuals as a function of several predictor variables, and also the general predictor variable
scaling of the various models. Secondly, the model exhibiting the best applicability to NZ was modified based on theoretical and empirically-driven
considerations to better represent the NZ data.